The discussion below is merely provided for general background information and is not intended to be used as an aid in determining the scope of the claimed subject matter.
The invention relates to a device for transferring personnel, equipment and/or structural elements from a surface vessel to an offshore structure, in particular a fixed offshore structure, such as a wind turbine, or to another vessel, the device comprising a foundation mounted or to be mounted on a surface vessel, an arm, e.g. a telescopic boom, pivotally connected to the foundation, e.g. via at least one gimbal or pair of gimbals, and at least one gripper connected to the free end of the arm for coupling the arm to an offshore structure. The invention further relates to a method of transferring personnel, equipment and/or structural elements.
It is known to provide access to a platform of an offshore wind turbine by providing e.g. rubber buffers on the front of a vessel such that the buffers of the vessel push against landing tubes on each side of a ladder of the turbine support to create enough friction to prevent movement, such as roll, heave or yaw, of the vessel relative to the support in three planes. Personnel can then transfer across the gap between the front of the vessel and the access ladder, i.e. across the so-called splash zone.
As explained in WO 2012/107459, this arrangement suffers from the drawback that the frictional force between the vessel and the support is highly variable, and is dependent upon the difference between the thrust generated by the vessel and the wave action on the hull of the vessel, as well as any material such as slime and barnacles adhering to the landing tubes. The available friction can also be reduced as a result of roll of the boat, and it is necessary for personnel to step between the ladder and the vessel which is moving relative to the support of the wind turbine, making transfer hazardous, especially in rough seas.
One known attempt to overcome this problem consists of an access apparatus mounted to a vessel and having a platform for personnel which moves relative to the vessel to compensate for motion of the vessel relative to the turbine support, so that the platform is substantially stationary relative to the support of the wind turbine. However, this arrangement suffers from the drawback that the apparatus requires much power, is expensive to acquire and run, and requires a large vessel to accommodate it.
WO 2012/107459 relates to an access apparatus (numeral 2 in the Figures of WO 2012/107459) for enabling transfer of personnel between a seaborne vessel (6) and an offshore installation. The apparatus comprises a body (18) adapted to be mounted to a deck (4) of a seaborne vessel, clamping members (10) adapted to grip a buffer tube, mounted to a support of an offshore installation, therebetween, to limit vertical movement of the buffer tube relative to the clamping members, wherein the clamping members can pivot relative to the body about a respective single pivot axis extending in at least two mutually perpendicular directions.
WO 02/20343 relates to a vessel provided with a telescopingly extendable gang plank mounted thereon for movement about a vertical axis. A coupling device provided at the free end of the gang plank is adapted to enclose a vertically directed engagement rod on an offshore pole body and thus connect the ship to the pole body. With the ship manoeuvred in a certain position the gang plank may be either directed and extended towards the engagement rod or be manoeuvred while taking its extended position laterally into contact with the engagement rod and subsequently (partially) retracted again.
WO 2012/069835 relates to a lift (2) to enable access between a waterborne vessel (1) and a structure (30). In an embodiment shown in FIG. 3 of WO 2012/069835 “The access lift 2 further comprises a base 5 . . . which supports the lift shaft assembly 3 (and the platform 4). . . . damped roller assembly 10 further comprises a yoke beam 15, to which the rollers 11 are rotatable mounted. . . . The yoke beam 15 further supports an actuated arm 16 for each of rollers 12, . . . ” The yoke beam (15) is also attached to the base (5), i.e., the arm (16) and the lift shaft assembly (3) are both attached to the base, not to each other.